Variable resistance



E. G; DANIELSON.

VARIABLE RESISTANCE. 3 APPLICATION FILED FEB- 14, l92l- 1,426,465. Patented Aug. 22, 1922;

WITNESS K INVENTOR f M V v E.6.VAN|e|.soN-

A TTORNE YS v UNITED STATES PATENT OFFICE.

ERNEST G. D NIELsoN. or sAN FRANCISCO, CALIFORNIA, ASSIGNOB T0 ELMER 'r.

k CUNNINGHAM, or sAN FRANCISCO, CALIFORNIA.

VARIABLE RESISTANCE.

Specification of Letters Patent.

Patented Aug. 22, 1922.

Application filed February 14, 1921. Serial No. 444,997.

tion.

The invention relates to a- Composition of matter, useful for providing an electric 're-' sistance device, and more particularly to a variable resistance which may be used in a potentiometer.

An object of the invention visto provide a variable resistance device of the poten-.

tiometer type in which a metal. to metal electrical contact is made between the contact arm and the variable resistance element;

Another object of the invention is to provide a new and useful composition of matter.

Still another object is to provide an inexpensive and reliable resistance element.-

Still another object of the invention is to provide a simple and inexpensive variable resistance device so constructed that for the same adjustment of the contacts. the value of the resistance thus chosen cannot be interfered with by such effects as variable contact resistances or loose contacts. Heretofore, variable resistance devices of this nature have comprised a strip of pressed or molded graphite over which a carbon button carried by the contact arm is movable. The resist ance of the contact between the button and the strip is variable due to variable conditions of pressure, surface condition of the strip and other causes,-so that for any iven adjustment of the contact button, diderent resistances are obtainedat different times. In the variable resistance lof my invention, the contact between the variable resistance and the contact arm is metal to metal. so

that the contact resistance remains constant, producing the same reslst-ance each time that the arm is moved to a'given ad- "justment, Further, graphite resistance elements are quite brittle and are subject to frequent breakage. whereas the device of my invention is comparatively unbreakable.

The invention possesses other advantageous features, some of which, with the foregoing, will be set forth atlength in the following description where I shall outline in full, that form of the invention which I have selected for illustration in the drawings accompanying and forming part of the present specification. In said drawings,

I have shownone embodiment of my in-.

vention, but it is to be understood that I do not limit myself to such form, since the Invention as set forth in the claims, may

.be embodied in a plurality of forms.

Referring to said drawings:

Figure 1 is an elevation of the device of my invention mounted on a panel.

Figure 2 is a cross section of the device taken on the line 2-2, Fig. 1.

The variable resistance-element comprises a strip or bar 3, of conduc-tivematerial,

which may be formed in any desired shape, 7

either straight or arcuate,'as shown. The bar Is composed. of. a homogeneous mixture of a blnder, Wl'llCh 1s preferably a. non-conductor, and a finely divided material, such as graphite, which is a conductor. The binder should be a material which hardens readily, either of its own accord or as the result of treatment, and which When hard produces a. strong bar. The binder which I prefer to employ is a synthetic gum, such as bakelite, which hardens 'under certain conditions of pressure and temperature. I have found also that an inert material, such as wood pulp, may be combined in the mixture, thus producing a saving in the amount of bakelite which must be used. In making the material, I usually employ equal amounts of bakelite m and wood pulp and to this I add suflic-ient finely divided graphite, to give the bar the de-' sired electrical conductance. The materials are thoroughly mixed to produce a hoinogeneous mixture, which it then placed in suitable molds and subjected to heat and bar, and projecting slightly therefrom on the outer surface, are

a series of metallic contacts 4, spaced apart regularlyfii'nd usually in the shape of cylin drlcal pins. These contact pins make permanent and unvarying contact with the that its end, which is preferably provided with a turned down tongue 12, makes pressure contact with the contacts 4. The end of the contact arm moves in the path of the series of contacts and is preferably of such.

size that it may bridge two adjacent contacts. At the ends, the bar is provided with integral stops 13, to limit the movement of the contact arm.

I claim:

1. A resistance element, comprising a molded mixture of a finely divided conducting material and a synthetic gum which hardens in molding.

2. A resistance element, comprising a molded mixture of finely divided graphite and a synthetic gum which hardens in molding.

3. A resistance element, comprising a molded mixture of finely divided graphite and ba-kelite type gum.

4. A resistance element, comprising a bakelite bar having finely divided graphite embedded therein.

5. A resistance element, comprisin a molded mixture of finely divided grapfiite, a neutral filler and a synthetic gum which hardens in molding.

6. A resistance element, comprising a molded mixture of finely divided graphite, wood pulp and a synthetic gum ,which hardens in molding.

7. A resistance element, comprising a molded mixture of finely divided graphite wood pulp and bakelite. type gum.

8. A resistance element, comprising a molded bakelite bar having Wood pulp and finely divided graphite embedded therein.

9. A variable resistance element, comprising a molded conductive bar having metallic contact pins embedded therein.

10. A variable resistance device, comprising a molded conductive bar, metallic contact pins embedded in said bar and a metallic contact movable over and in contact with said pins.

11. A variable resistance element, comprising a molded barcontaining graphite and bakelite, metallic contacts molded in said bar and a metallic contact arm movable in contact with saidcontacts.

12. A variable resistance device, comprising an arcuate molded conductive bar, metallic contact pins molded in said bar, and a resilient metallic cont-act arm movable in contact with said contacts.

13. A composition of matter comprising a homogeneous mixture of non-conducting moldable material and finely divided conductin material.

14. composition of matter comprising a homogeneous mixture of non-conducting moldable material and finely divided graphite.

In testimony whereof, I have hereunto set 

